Plant Molecular Biology

, Volume 63, Issue 2, pp 257–271

The Arabidopsis stearoyl-acyl carrier protein-desaturase family and the contribution of leaf isoforms to oleic acid synthesis



In plants, changes in the levels of oleic acid (18:1), a major monounsaturated fatty acid (FA), results in the alteration of salicylic acid (SA)- and jasmonic acid (JA)-mediated defense responses. This is evident in the Arabidopsisssi2/fab2 mutant, which encodes a defective stearoyl-acyl carrier protein-desaturase (S-ACP-DES) and consequently accumulates high levels of stearic acid (18:0) and low levels of 18:1. In addition to SSI2, the Arabidopsis genome encodes six S-ACP-DES-like enzymes, the native expression levels of which are unable to compensate for a loss-of-function mutation in ssi2. The presence of low levels of 18:1 in the fab2 null mutant indicates that one or more S-ACP-DES isozymes contribute to the 18:1 pool. Biochemical assays show that in addition to SSI2, four other isozymes are capable of desaturating 18:0-ACP but with greatly reduced specific activities, which likely explains the inability of these SSI2 isozymes to substitute for a defective ssi2. Lines containing T-DNA insertions in S-ACP-DES1 and S-ACP-DES4 show that they are altered in their lipid profile but contain normal 18:1 levels. However, overexpression of the S-ACP-DES1 isoform in ssi2 plants results in restoration of 18:1 levels and thereby rescues all ssi2-associated phenotypes. Thus, high expression of a low specific activity S-ACP-DES is required to compensate for a mutation in ssi2. Transcript level of S-ACP-DES isoforms is reduced in high 18:1-containing plants. Enzyme activities of the desaturase isoforms in a 5-fold excess of 18:1-ACP show product inhibition of up to 73%. Together these data indicate that 18:1 levels are regulated at both transcriptional and post-translational levels.


SSI2/FAB2 Stearoyl-ACP-Desaturase Oleic acid Salicylic acid Jasmonic acid 





Fatty acid


Oleic acid


Stearic acid



Supplementary material

11103_2006_9086_MOESM1_ESM.tif (337 kb)
Supplementary material
11103_2006_9086_MOESM2_ESM.pdf (137 kb)
Supplementary material
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Supplementary material

Copyright information

© Springer Science+Business Media B.V. 2006

Authors and Affiliations

  • Aardra Kachroo
    • 1
  • John Shanklin
    • 2
  • Edward Whittle
    • 2
  • Ludmila Lapchyk
    • 1
  • David Hildebrand
    • 3
  • Pradeep Kachroo
    • 1
  1. 1.Department of Plant PathologyUniversity of KentuckyLexingtonUSA
  2. 2.Department of BiologyBrookhaven National LaboratoryUptonUSA
  3. 3.Department of Plant and Soil SciencesUniversity of KentuckyLexingtonUSA

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